RESUMEN
ß-dystroglycan (ß-DG) is a key component of multiprotein complexes in the plasma membrane and nuclear envelope. In addition, ß-DG undergoes two successive proteolytic cleavages that result in the liberation of its intracellular domain (ICD) into the cytosol and nucleus. However, stimuli-inducing ICD cleavage and the physiological relevance of this proteolytic fragment are largely unknown. In this study we show for the first time that ß-DG ICD is targeted to the nucleolus where it interacts with the nuclear proteins B23 and UBF (central factor of Pol I-mediated rRNA gene transcription) and binds to rDNA promoter regions. Interestingly DG silencing results in reduced B23 and UBF levels and aberrant nucleolar morphology. Furthermore, ß-DG ICD cleavage is induced by different nucleolar stressors, including oxidative stress, acidosis, and UV irradiation, which implies its participation in the response to nucleolar stress. Consistent with this idea, overexpression of ß-DG elicited mislocalization and decreased levels of UBF and suppression of rRNA expression, which in turn provoked altered ribosome profiling and decreased cell growth. Collectively our data reveal that ß-DG ICD acts as negative regulator of rDNA transcription by impeding the transcriptional activity of UBF, as a part of the protective mechanism activated in response to nucleolar stress.
Asunto(s)
Nucléolo Celular/metabolismo , Distroglicanos/metabolismo , Proteínas del Complejo de Iniciación de Transcripción Pol1/metabolismo , ARN Ribosómico/biosíntesis , Animales , Proliferación Celular/genética , Citoplasma/metabolismo , ADN Ribosómico/genética , ADN Ribosómico/metabolismo , Distroglicanos/antagonistas & inhibidores , Distroglicanos/genética , Ratones , Mioblastos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Nucleofosmina , Estrés Oxidativo , Proteínas del Complejo de Iniciación de Transcripción Pol1/genética , Dominios Proteicos/genética , ARN Ribosómico/genética , Ribosomas/metabolismo , Transcripción Genética , Regulación hacia Arriba/genéticaRESUMEN
Dystroglycan has recently been characterized in blood tissue cells, as part of the dystrophin glycoprotein complex but to date nothing is known of its role in the differentiation process of neutrophils. We have investigated the role of dystroglycan in the human promyelocytic leukemic cell line HL-60 differentiated to neutrophils. Depletion of dystroglycan by RNAi resulted in altered morphology and reduced properties of differentiated HL-60 cells, including chemotaxis, respiratory burst, phagocytic activities and expression of markers of differentiation. These findings strongly implicate dystroglycan as a key membrane adhesion protein involved in the differentiation process in HL-60 cells.